This invention relates in general to machines for working sheet metal, and more particularly to a machine for bending reverse flanges or cleat edges on sheet metal.
The duct work in most residential, commercial and industrial buildings is formed from sheet metal with each duct consisting of individual duct sections coupled together at their ends. To join the sections together, corresponding end walls on adjacent duct sections are provided with reverse flanges, called cleat edges, and an interlocking drive cleat is passed over the cleat edges to prvent them and the duct sections of which they form a part from pulling away from each other.
While cleat edges may be formed on ducts by a hand operation, it is difficult to form evenly and correctly gauged cleat edges in such a manner. Moreover, hand forming is quite time consuming. To simplify the cleat edge forming operation, machines have been developed for this purpose. One such machine is disclosed in U.S. Pat. No. 2,973,796. That machine utilizes two bars which engage the end of a duct wall in sequence. The first bars turns the duct wall 90.degree., while the second bar thereafter turns it another 90.degree. so that as to impart a 180.degree. turn to the wall at its end. However, before first bar is engaged with the wall, a gauge must be positioned beyond the end of the duct and the end wall brought against that gauge. This positions the duct so that the bars will engage the proper amount of metal, thus insuring that the cleat edge which is formed possesses the proper width. Gauging in this manner introduces an additional step into the procedure, and if this step is not performed or is performed incorrectly, the machine may jam. Furthermore, once the duct is formed by the machine, the duct is more or less interlocked with the machine and is quite difficult to remove. Aside from the foregoing, the rotating bars must be quite thin so as not to interfere with each other, and as a result, they are not very rigid in extended lengths. As a practical matter, the bars cannot be made much longer than about 24 inches, so these machines cannot be used with ducts greater than 24 inches in width.